Authors: Cacabelos, Ramon; Llovo, Ruth; Fraile, Carmen; Fernandez-Novoa, Lucia

Source: Current Alzheimer Research, Volume 4, Number 4, September 2007 , pp. 479-500(22)

Publisher: Bentham Science Publishers

Abstract:

Recent studies demonstrate that the therapeutic response in Alzheimer's disease (AD) is genotype-specific. More than 200 genes are potentially associated with AD pathogenesis and neurodegeneration, and approximately 1,400 genes distributed across the human genome account for 20 to 95% of variability in drug disposition and pharmacodynamics. Cytochrome P450 enzymes encoded by genes of the CYP superfamily, such as CYP1A1 (15q22-q24), CYP2A6 (19q13.2), CYP2C8 (10q24), CYP2C9 (10q24), CYP2C19 (10q24.1-q24.3), CYP2D6 (22q13.1), CYP2E1 (10q24.3-qter), and CYP3A5 (7q22.1), acting as terminal oxidases in multicomponent electron transfer chains which are called P450- containing monooxygenase systems, metabolize more than 90% of drugs. Some of the enzymatic products of the CYP gene superfamily can share substrates, inhibitors and inducers whereas others are quite specific for their substrates and interacting drugs. Some cholinesterase inhibitors (tacrine, donepezil, galantamine) are metabolized via CYP-related enzymes, especially CYP2D6, CYP3A4, and CYP1A2. The distribution of CYP2D6 genotypes in the Spanish population is the following: (a) Extensive Metabolizers (EM)(51.61%): *1/*1, 47.10%; and *1/*10, 4.52%; (b) Intermediate Metabolizers (IM)(32.26%): *1/*3, 1.95%; *1/*4, 17.42%; *1/*5, 3.87%; *1/*6, 2.58%; *1/*7, 0.75%; *10/*10, 1.30%; *4/*10, 3.23%; *6/*10, 0.65%; and *7/*10, 0.65%; (b) Poor Metabolizers (PM)(9.03%): *4/*4, 8.37%; and *5/*5, 0.65%; and (c) Ultrarapid Metabolizers (UM)(7.10%): *1xN/*1, 4.52%; *1xN/*4, 1.95%; and CYP2D6 gene duplications, 0.65%. PMs and UMs also accumulate genotypes of risk associated with APOE-, PS-, ACE-, and PRNP-related genes. Approximately, 15% of the AD population may exhibit an abnormal metabolism of cholinesterase inhibitors; about 50% of this population cluster would show an ultrarapid metabolism, requiring higher doses of cholinesterase inhibitors to reach a therapeutic threshold, whereas the other 50% of the cluster would exhibit a poor metabolism, displaying potential adverse events at low doses. In AD patients treated with a multifactorial therapy, including cholinesterase inhibitors (e.g., donepezil), the best responders are the CYP2D6-related EMs and IMs, and the worst responders are PMs and UMs. In addition, the presence of the APOE-4 allele in genetic clusters integrating CYP2D6 and APOE genotypes contributes to deteriorate the therapeutic outcome. From these data, it can be postulated that pharmacogenetic and pharmacogenomic factors are responsible for 75-85% of the therapeutic response in AD patients treated with conventional drugs.

Keywords: Alzheimer's disease; genetics; genomics; multifactorial treatment; cholinesterase inhibitors; APOE; CYP2D6; pharmacogenetics; pharmacogenomics

Document Type: Research article

DOI: http://dx.doi.org/10.2174/156720507781788846

Publication date: 2007-09-01

More about this publication?

• Current Alzheimer Research publishes peer-reviewed frontier review and research articles on all areas of Alzheimer's disease. This multidisciplinary journal will help in understanding the neurobiology, genetics, pathogenesis, and treatment strategies of Alzheimer's disease. The journal publishes objective reviews written by experts and leaders actively engaged in research using cellular, molecular, and animal models. The journal also covers original articles on recent research in fast emerging areas of molecular diagnostics, brain imaging, drug development and discovery, and clinical aspects of Alzheimer's disease. Manuscripts are encouraged that relate to the synergistic mechanism of Alzheimer's disease with other dementia and neurodegenerative disorders. Book reviews, meeting reports and letters-to-the-editor are also published. The journal is essential reading for researchers, educators and physicians with interest in age-related dementia and Alzheimer's disease. Current Alzheimer Research provides a comprehensive 'bird's-eye view' of the current state of Alzheimer's research for neuroscientists, clinicians, health science planners, granting, caregivers and families of this devastating disease.

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